Critical role of carbon support in metal nanoaggregate facilitating Fe-N-C catalyst for PEM fuel cell application

Metal nanoaggregates can simultaneously enhance the activity and stability of Fe-N-C catalysts in proton-exchange-membrane fuel cells (PEMFC). Previous studies on the relevant mechanism have focused on the direct interaction between FeN₄ active sites and metal nanoaggregates. However, the role of carbon support that hosts metal nanoaggregates and active sites has been overlooked. Here, a Fe-N-C catalyst encapsulating inactive gold nanoparticles is prepared as a model catalyst to investigate the electronic tuning of Au nanoparticles (NPs) towards the carbon support. Au NPs donate electrons to carbon support, making it rich in π electrons, which reduces the work function and regulates the electronic configuration of the FeN₄ sites for an enhanced ORR activity. Meanwhile, the electron-rich carbon support can mitigate the electron depletion of FeN₄ sites caused by carbon support oxidation, thereby preserving its high activity. The yield and accumulation of H₂O₂ are thus alleviated, which delays the oxidation of the catalyst and benefits the stability. Due to the electron-rich carbon support, the composite catalyst achieves a top-level peak power density of 0.74 W/cm² in a 1.5 bar H₂-air PEMFC, as well as the improved stability. This work elucidates the key role of carbon support in the performance enhancement of the Fe-N-C/metal nanoaggregate composite catalysts for fuel cell application.